1. Technical Field of the Invention
The present invention relates to a drive unit in which an electric motor is used as a power source, and more particularly, to a cooling system in a drive unit for an electric vehicle or a hybrid drive unit.
2. Related Art
When an electric motor is used as a power source for a vehicle, the load exerted on the electric motor varies significantly with running conditions. Accordingly, in order to manage the heat generation with a heavy load, cooling is necessary. Therefore, conventionally, as disclosed in Japanese Patent Application Laid-Open No. 7-288949, the drive unit case is provided with a water passage for cooling the electric motor.
However, in the conventional system, the coolant passage is formed as tubing held in a spiral groove on the outer surface of the casing, with substantially half of the circular section of the tubing exposed and extending from the outer surface of the casing. Such structure is complicated, and is disadvantageous in terms of cost and space.